Ranitidine is, chemically, N-[2-[[[5-[(dimethylamino)methyl]-2-furanyl]methyl]thio]ethyl]-N'-methyl-2 -nitro-1,1-ethene diamine, and has the chemical structural formula: ##STR1##
In the form of its hydrochloride salt, ranitidine has achieved widespread acceptance as a medicament for treating ulcers.
The patent and technical literature concerning ranitidine hydrochloride reports that it exists in two different crystalline forms, Form 1 and Forth 2. The preparation and characteristics of ranitidine hydrochloride Form 2, which is the commercially marketed form, are described in Canadian Patent no. 1,202,638 Crookes, assigned to Glaxo Group Limited, and issued Apr. 1, 1986. In this patent disclosure, ranitidine hydrochloride Form 1 is reported to be formed by precipitation and crystallization from a solution of ranitidine in industrial methylated spirit containing hydrogen chloride, by addition of ethyl acetate thereto. It is also reported therein that Form 1 ranitidine hydrochloride so produced has unsuitable filtration and drying characteristics, and that Form 2 ranitidine hydrochloride has more advantageous properties, and better characteristics from a manufacturing point of view. This Form 2 ranitidine hydrochloride is reportedly obtained by appropriately chosen crystallization processes. One of these is dissolving the free base in a hydroxylic solvent such as propan-2-ol and treating the solution with hydrochloric acid, followed by crystallization at an elevated temperature by adding further quantities of propan-2-ol. Another is dissolving Form 1 ranitidine hydrochloride in methanol or ethanol with warming, followed by cooling to cause crystallization of the Form 2 salt, optionally accompanied by the addition of an anti-solvent or accompanied by seeding with Form 2 ranitidine hydrochloride crystals.